1. Field of the Invention
This invention relates to the regeneration of catalysts containing various metal oxides by impregnating the spent catalyst with a solution containing a combination of metals. More particularly, a catalyst for the production of acrylonitrile from propylene, ammonia and oxygen or air (ammoxidation) comprising the oxides of potassium, cobalt, nickel, iron, bismuth, phosphorus and molybdenum is regenerated by impregnating the spent catalyst with a solution comprising soluble molybdenum and bismuth species and thereafter calcining the treated catalyst to obtain an active catalyst.
2. Description of the Prior Art
It is known that certain molybdenum-containing catalysts which are especially adapted for ammoxidation tend to deactivate upon prolonged exposure to reactants at reaction conditions. It has also been observed that molybdenum is lost from the catalyst during reaction. In Dutch Pat. No. 7,411,063 it is suggested that one deactivation path is the loss of molybdenum and suggests the catalyst be reactivated in situ, i.e. without removal from the reactor, by contacting the ammoxidation catalyst with fluid-bed particles of molybdenum on an inert support. Optionally, the particles can contain other elements such as iron, bismuth or tellurium which may be useful in the regeneration, but particles consisting essentially of molybdenum on an inert support are preferred. The preferred method for preparing the particles involves spray drying an aqueous slurry containing the finely divided support material and finely divided molybdenum metal or molybdenum compound. An alternate preparation involves combining a solution of a molybdenum compound with a finely divided support material and thereafter drying and grinding the particles.
German Offenlegungschrift 2,352,196, published on Oct. 18, 1973, discloses a process for regenerating a catalytic matrix containing the oxides of cobalt and molybdenum, magnesium and molybdenum, nickel and molybdenum, manganese and molybdenum or mixtures thereof by impregnating the catalyst with a liquid containing compounds of bismuth, iron, tellurium or mixtures thereof that are at least partially soluble in the liquid and thereafter heating the impregnated matrix at an elevated temperature to form an active catalyst.
The regeneration of catalysts containing iron and molybdenum to restore lost molybdenum by impregnating the spent catalyst with a solution of an amine molybdate (a nonoxidizing compound of molybdenum), removing the solvent and further heating the catalyst is disclosed in U.S. Pat. No. 2,973,326, issued on Feb. 28, 1961.
The incorporation of iron into a spent bismuth phosphomolybdate catalyst to increase the activity thereof is disclosed in U.S. Pat. No. 3,629,148 issued on Dec. 21, 1971 and/or U.S. Application Ser. No. B260,945 published on Jan. 28, 1975.